The $\hbox {Co}^{2+}$ Reduction on the Hetero-System $\hbox {CuFe}_{2} \hbox {O}_{4}/\hbox {SnO}_{2}$ Under Solar Light

Abstract

The $\hbox {Co}^{2+}$ reduction on the hetero-system $\hbox {CuFe}_{2} \hbox {O}_{4}/\hbox {SnO}_{2}$ under solar light is reported for the first time. The spinel $\hbox {CuFe}_{2} \hbox {O}_{4}$, prepared by co-precipitation, is characterized photoelectrochemically, and the conduction band ($-1.63 \hbox { V}_{SCE}$) is more cathodic than the $\hbox {Co}^{2+}$ level. $\hbox {SnO}_{2}$, synthesized by chemical route, is used as electrons bridge to mediate the electron transfer. The photocatalysis is investigated in batch mode by varying the catalyst dose, the $\hbox {Co}^{2+}$ concentration and pH. Reduction efficiency of 62% is obtained under sunlight ($102\,\hbox {mW cm}^{-2}$) and optimal conditions ($\hbox {Co}^{2+}: 50\,\hbox {mg L}^{-1}, \hbox { pH } \sim 5.5, \hbox {CuFe}_{2} \hbox {O}_{4}/\hbox {SnO}_{2}: 1/1$). The reduction follows a zero-order kinetic with a rate constant of $0.29\,\hbox {mol L}^{-1} \,\hbox {mn}^{-1}$. The decrease in the conversion rate over illumination time is due to the competitive hydrogen formation on ultrafine co-clusters. $\hbox {H}_{2}$ evolution rate of $0.19 \, \upmu \hbox {mol}\,(\hbox {mg catalyst})^{-1}\,\hbox { mn}^{-1}$ under artificial light ($29\,\hbox {mW cm}^{2}$) is obtained.